Pd-based bimetallic catalysts for parahydrogen-induced polarization in heterogeneous hydrogenations

Production of hyperpolarized catalyst-free gases and liquids by heterogeneous hydrogenation with parahydrogen can be useful for various technical as well as biomedical applications, including in vivo studies, investigations of mechanisms of industrially important catalytic processes, enrichment of nuclear spin isomers of polyatomic gases, and more. In this regard, the wide systematic search for heterogeneous catalysts effective in pairwise H2 addition required for the observation of parahydrogen-induced polarization (PHIP) effects is crucial. Here in this work we demonstrate the competitive advantage of Pd-based bimetallic catalysts for PHIP in heterogeneous hydrogenations (HET-PHIP). The dilution of catalytically active Pd with less active Ag or In atoms provides the formation of atomically dispersed Pd1 sites on the surface of Pd-based bimetallic catalysts, which are significantly more selective toward pairwise H2 addition compared to the monometallic Pd. Furthermore, the choice of the dilution metal (Ag or In) has a pronounced effect on the efficiency of bimetallic catalysts in HET-PHIP, as revealed by comparing Pd-Ag and Pd-In bimetallic catalysts.</p

Single-Site Heterogeneous Catalysts and Photocatalysts for Emerging Applications

Single-site heterogeneous catalysts and photocatalysts have received great attention in recent years, which is due to their superior activity and selectivity values achieved in numerous applications. Aside from the excellent performance displayed by virtue of their intrinsic properties, they are also promising from the elemental sustainability standpoint. Single-site systems possess well-defined active centers with unique and identical behavior, which allows for the precise determination of structure-activity relationships as well as mechanism investigation. The design and development of single-site-based catalysts and photocatalysts are fascinating yet challenging, since those active centers might lack stability under reaction conditions because of their tendency to evolve, forming larger clusters and nanoparticles, so the selection of a suitable support matrix is highly desirable. In this chapter, representative examples of single-site catalysts and photocatalysts are included by pointing out their superior performance in important applications of diverse type. For the catalytic systems, examples of Au-, Pt-, and Pd-based catalysts are briefly described, while highlighting the role of the support in affording stable catalytic centers with outstanding performance in several applications, such as CO oxidation, water-gas shift reaction, hydrogenation reactions, and production of hydrogen. Further, the photocatalytic systems of Ti, Cr, and V-oxide moieties incorporated in porous frameworks of silica and zeolites are discussed for their catalytic applications in NO decomposition, CO2 reduction, partial oxidation of hydrocarbons, and alkene epoxidation under UV and visible-light irradiation.</p